Have never seen a slug mold for a 410. But if your not opposed to shooting R.ball from your 410. Ballistic Products here in MN sell a ball/ sabot combo for 410 ga. I use them myself for yard varmints. There fun to shoot. Sabots are made for 2-1/2" hulls. But I relaod them into 3" with an extra over powder wad from Circle Fly Wads. (click links enclosed)
ballisticproducts.com/Slugs-and-Components/products/71/
www.circlefly.com/index.html